This invention relates to herbicidal compositions, their methods of use, and their preparation. In particular, this invention relates to herbicidal compositions comprising an herbicidally active thiocarbamate in combination with certain unsaturated aryl sulfides, sulfoxides and sulfones, the latter serving to prolong the effectiveness of a single application of the thiocarbamate in controlling undesired plant growth.
Many of the compounds herein disclosed are known compounds, however, one of the compounds herein exemplified, namely, 4-methoxyphenyl-1-propynyl sulfide having the formula ##STR2## is a novel compound. Most of the references which have disclosed compounds within the generic formula of the instant invention, show their utility to be only as chemical intermediates in various syntheses. Martin et al., U.S. Pat. No. 3,777,024, discloses some aryl propargyl sulfides as insecticidal synergists, and Martin et al., South African Pat. No. 28,150, discloses such compounds as endo- and ectoparasiticides. Neither patent discloses such compounds in combination with thiocarbamate herbicides, or as having any soil extender properties for any herbicides.
Thiocarbamates are well known in the agricultural art as herbicides useful for weed control in crops such as corn, potatoes, beans, beets, spinach, tobacco, tomatoes, alfalfa, rice and others. Thiocarbamates are primarily used in pre-emergence application, and are particularly effective when incorporated into the soil prior to the planting of the crop. The concentration of the thiocarbamate in the soil is greatest immediately after application of the compound. How long thereafter the initial concentration is retained depends in large part on the particular soil used. The rate at which the thiocarbamate concentration declines following its application varies from one type of soil to the next. This is evident both in the observable extent of weed control and in the detectable presence of undegraded thiocarbamate remaining in the soil after considerable time has elapsed.
It is therefore an object of this invention to increase the soil persistence of thiocarbamate herbicides and thus improve their herbicidal effectiveness.